1. Field of the Invention
The present invention relates to an output system of image data stored in an image memory.
2. Description of the Prior Art
In the image expression using an intermediate gradient coding system for expressing an intermediate gradient image of 2.sup.n gradients by n bits, the quantity of the image data of one line in the main scanning direction is constant irrespective of an image pattern. For example, in the case where one pixel is expressed by four bits (16 gradients) assuming that the resolution in the main scanning direction is 8 PEL, the quantity of all data of one line of an original of the A4 size is 216.times.8.times.4=6912 bits. When it is assumed that the length in the sub-scanning direction of the original is 297 mm and the resolution is 8 line/mm, the whole data quantity per one sheet of the A4-size original is 6912.times.297.times.8.apprxeq.16,422,912 bits. Thus, at least about 24 bits are needed as a storage address to store such a great amount of data in a conventional memory or the like and to control these data.
It is now assumed that an image data of one page has been stored from addresses A to B in an image memory, in the case where the image data is recorded on the standard-scale recording paper of the A4 size, a discrimination is made to see if this image data of one page can be recorded on the single standard-scale recording paper or not by calculating B-A. If B-A is larger than 16,422,912 bits, the image data cannot be recorded on the one standard-scale recording paper, so that the data in the image memory has to be again read out from the address (A+16,422,912) to record the image data on the second standard-scale recording paper. To execute the above-mentioned operation, the 24-bit operation has to be performed with respect to all data. However, the 24-bit CPU (Central Processing Unit) is expensive and the arrangement of this unit becomes very complicated. In the foregoing intermediate gradient coding system, one pixel is expressed by the data amount of four bits; therefore if the address is shifted by merely one bit when the head pixel information is read out from the image memory, the information of the next pixel and of the subsequent pixels is unreliable. Thus, it is difficult to simplify the address control of the image memory.